The present embodiments relate to a magnetic resonance tomography (MRT) local coil for an MRT system.
Magnetic resonance tomography devices for examination of objects or patients by magnetic resonance tomography (e.g., MRT, MRI, MR) are known, for example, from DE10314215B4.
In MR tomography, images with a high signal-to-noise ratio (SNR) may be recorded with coils or local coils. The coils or local coils are antenna systems that are attached in the immediate vicinity on (e.g., anterior) or below (e.g., posterior) the patient. In an MR measurement, excited nuclei (e.g., in a recording area in the object under examination) induce voltages in each case in the individual antennas of the local coil. The induced voltages are amplified with a low-noise preamplifier (e.g., LNA, Preamp) and are transferred via a cable, for example, to receive electronics. To improve the signal-to-noise ratio, even in high-resolution images, for example, high field systems are used as MRTs (e.g., 1.5 T to 12 T and more). Since more individual antennas may be connected to an MRT receive system than there are receivers present, a switching matrix (e.g., an RCCS) is installed between receive antennas and receivers. This routes the currently active receive channels (e.g., the receive channels that lie right in the field of view (FoV) of the magnet/MRT) onto the available receivers. More coil elements than there are receivers present may be connected, since for whole body coverage, only the coil elements that are located in the FoV and/or in the homogeneity volume of the magnet of the MRT are to be read out.
“Coil” (e.g., local coil) refers to an antenna system (e.g., an array coil) that may include one or more antenna elements (e.g., coil elements). The individual antenna elements may be embodied as loop antennas (e.g., loops) or butterfly coils. A coil includes coil elements, a preamplifier, further electronics (e.g., sheath wave filters) and cabling, the housing and, for example, a cable with a plug connector, through which the coil is connected to the MRT system. A receiver (RX) attached to the system side filters and digitizes signals received from the local coil and transfers generated data based thereon to a digital signal processor. The digital signal processor may derive an image or a spectrum from the measurement and makes the image or the spectrum available to the user for diagnosis.
To achieve a high SNR, the antenna elements are attached as close as possible to the patient contour of the patient to be examined. The interior space of an MR head coil may be small, for example. This is provided for high-channel coils, of which the smaller antenna elements possess a smaller optimal penetration depth than other local coils (e.g., with fewer coil elements).
One objective is, despite a smaller coil interior space, to achieve the greatest possible patient coverage (e.g., suitability for 80-95% of patients). The face and chest area of a patient exhibits a large variance. This provides that neck coils resting closely on the patient collide at a steeply rising neck-chest transition of the patient with the chest and are thereby not able to be used. Collisions with the chin of the patient or with the nose are also possible.
This may occur with stoutly built patients with a large-volume upper back part, since when these patients lay down, the head falls into the nape of the neck, and the chin is located at a relatively high position in the coil. This leads to the upper part of the head coil (e.g., also the head/neck coil upper section) not being able to be closed as desired. The forehead area is less problematic because of the smaller variance. The height differences are around 1-2 cm, whereas differences arise in the nose area of 2-3 cm, and in the chin and chest area of more than 5 cm. The width of the head coil is less problematic because of the almost constant shape of the head.
Known head coils or head and neck coils have fixed, non-size-adjustable housings and are dimensioned, depending on design and customer requirement, to achieve 80%-95% patient coverage.
This provides that SNR is “given away” at different points because the coils are dimensioned for slightly larger heads. Sufficient space is held in reserve in the nose, chin and upper chest area because of the greater variance in this area.
A size-adjustable head coil is described in patent application DE102006027189A1, which, for example, may move a head coil upper part in the back of the head-forehead area (e.g., the y direction). This helps to increase the space for chin and nose and also increases the distance of the antenna from the forehead and the front area of the skull.